Software emulated switching of dual network devices

ABSTRACT

In an environment comprising a group of servers and at least two network devices, a link fault is detected. A data cable connects each of the servers to both network devices. An active communication path from one of the network devices to the servers is determined. In response to detecting a failure of the active communication path, a second of the network devices is indicated as the active network device. The configuration is detected by the network devices based on packets received at the network devices.

BACKGROUND

A data center is a facility that houses computer systems and various networking, storage, and other related components. Data centers may, for example, provide computing services to businesses and individuals as a remote computing service or provide “software as a service” (e.g., cloud computing).

A data center may house hundreds or thousands of servers. Each server may host a number of virtual machines and other resources. It is important to prevent downtime due to hardware and network failures and other issues that may prevent the operation of services provided by the data center. Some data centers may implement ways to provide some resiliency to failures that might prevent a loss of network communications. Such resiliency may exist from Tier-1 networking elements to the higher tier networking elements. However, since each individual server typically only uses a single connection to the first network element, referred to as a Tier-0 element (e.g., Top of Rack (ToR) device), there may be a single point of failure that may isolate a server or an entire rack of servers from the network.

When a data center experiences server connectivity issues, loss of data and services may result, preventing users from providing quality services to their downstream customers, which may result in lost revenue and customer dissatisfaction. Production loss and inefficiencies with respect to computing resources can be exacerbated when the data center is unable to quickly isolate and correct the cause of a connection failure. Additionally, scheduled maintenance and replacement of a Tier-0 device may require that the servers connected to that Tier-0 device lose connectivity while the Tier-0 device is being replaced or serviced. Many service agreements require that customers are given advance notice, thus precluding the possibility of scheduling maintenance as needed by the service provider without providing notice, or precluding the possibility of replacing the Tier-0 device on the spot.

It is with respect to these considerations and others that the disclosure made herein is presented.

SUMMARY

The disclosed embodiments describe technologies for providing an alternate low speed data path for devices connected to a network device such as a Tier-0 device to help prevent the devices from becoming isolated, for example from the main control plane network when the network device or connections to the network device are lost. The technologies may be implemented in conjunction with servers and other devices that require network resiliency, in particular when the devices do not require a high-speed redundant data link, such as for a control plane link.

Cloud service providers typically run workloads that are mission critical and are highly sensitive to link failures. In some cases, the cost of lost business may exceed the deployment costs when failures occur.

It may be possible to use a combination of Network Interface Card (NIC) teaming and multi-chassis link aggregation to provide a first and second interface into the network to guard against a single cable failure or single Tier-0 device failure. These methods may be suited for operating systems and applications that are configured to recognize the additional network resources and detect and respond to a failure in one of the network connections. However, NIC teaming and multi-chassis link aggregation may be difficult to implement for cloud-scale hosted virtual machine services because some operating systems and software applications may not be designed to recognize two network interfaces. Additionally, there may be issues with a possible loss of traffic forwarding capability that may be difficult to prevent and debug.

In some cases, in order to provide network resiliency down to the server level, it may be possible to connect each server to two different Tier-0 network elements through diversely routed facilities (e.g., optical or copper cables). However, providing a second NIC to each server may be costly when using custom NICs with complex acceleration logic.

It may also be possible to duplicate the network devices using a switch or multiplexer. However, this would require changes to the network device interfaces that may undermine compatibility between devices in a data center, as well as require the expense of custom switches or multiplexers that can greatly increase the cost of deploying such a solution across a data center or across multiple data centers.

The disclosed embodiments describe a way to respond to a failure of a network device or failed network facilities (e.g., cabling) and enable data traffic flows through the network so that normal data link availability may be quickly restored while avoiding significant impacts to the customers.

In an embodiment, a dual-redundant/switching cable is implemented that provides redundancy and operates with dual redundant network devices (e.g., ToRs) while lowering the cost of selecting and switching between the dual network devices. For example, an active direct attach cable (DAC) assembly is used to switch between dual ToRs. One end of the cable provides a standard NIC connector (e.g., QSFP28 or other) while the other end of the cable has an active multiplexer/switch that selects the active (primary) ToR. The cable multiplexer/switch can be commanded to switch between ToRs through a data bus or signal wire. Alternatively, a protocol such as Bidirectional Forwarding Detection (BFD) protocol can be used to detect a fault and determine whether to switch between ToRs.

On the ToR side, both ToRs may receive the same data from each connected server but only one (active or primary) ToR transmits data towards the host on the connected servers. In various embodiments, a way to implement dual active/passive ToRs without external changes to the ToRs is disclosed, thus reducing costs that would otherwise be required if the ToR were to be modified. Furthermore, the ToRs need not communicate with one another to arbitrate which one is primary and which one is the backup.

In some embodiments, the properties and utilities of network protocols such as Ethernet protocols may be used to enable a software-based primary/backup switching between ToRs by configuring the ToRs to detect their send/receive status and act accordingly. This allows the multiplexer of the redundant cable to be implemented as a switch or hub and treat the ToRs as nodes on the network. Data from the host may be transmitted as a broadcast on the network, so that both ToRs will receive the transmitted data. The network may use a utility for discovery and pinging lower layer devices on the network, such as ARPing. Ping packets may be transmitted on the link to probe hosts using Address Resolution Protocol (ARP). The pinged information allows for the association of the MAC address of the host and the receiving MAC address for the active ToR. This allows hosts to be resolved by their MAC addresses, and both ToRs can determine, based on the pinged information, whether they are an active or passive ToR. Thus, only traffic originating from the active ToR will be forwarded to the destination host.

Among many other benefits, the techniques shown herein improve efficiencies with respect to a wide range of computing resources. For instance, data centers may avoid or reduce the number of server connectivity issues and the resulting loss of data and services. Additionally, scheduled maintenance and replacement of Tier-0 devices may be performed without losing connectivity to the servers connected to that Tier-0 device. Additionally, data centers can perform such services without the requirement to provide advance notice to customers, thus providing greater efficiencies in scheduling maintenance or performing maintenance in quick response to incidents. Other technical effects, other than those mentioned herein, can also be realized from implementations of the technologies disclosed herein.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended that this Summary be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

DRAWINGS

The Detailed Description is described with reference to the accompanying figures. In the description detailed herein, references are made to the accompanying drawings that form a part hereof, and that show, by way of illustration, specific embodiments or examples. The drawings herein are not drawn to scale. Like numerals represent like elements throughout the several figures.

FIG. 1 is a diagram illustrating a data center for providing computing resources in accordance with the present disclosure;

FIG. 2A is an example resilient network topology in accordance with the present disclosure;

FIG. 2B is an example resilient network topology in accordance with the present disclosure;

FIG. 3A is an example resilient network topology in accordance with the present disclosure;

FIG. 3B is an example resilient network topology in accordance with the present disclosure;

FIG. 4 is a flowchart depicting an example procedure in accordance with the present disclosure;

FIG. 5 is a flowchart depicting an example procedure in accordance with the present disclosure;

FIG. 6 is a flowchart depicting an example procedure in accordance with the present disclosure;

FIG. 7 is an example computing device in accordance with the present disclosure.

DETAILED DESCRIPTION

The disclosed embodiments describe technologies for providing an alternate network path to prevent servers from becoming isolated from the main data and/or control network. In an embodiment, a multiplexer or switch device may be integrated with a cable, such as a DAC cable, which may be referred to herein as a dual cable. The multiplexer or switch device may be referred to herein as a switch device. In some embodiments, the dual cable may provide a cross-point switch capability that can switch traffic at OSI model Layer 1 (physical layer) between dual redundant Tier-0 devices, which in many examples herein can be a Top of Rack (ToR) device, and a server of a group of servers may be connected to the dual cable. In other examples, the dual cable may provide a cross-point switch capability that can switch traffic between other redundant network devices.

In one embodiment, the dual cable may interconnect one server of a rack to two ToRs. Multiple dual cables may be used to connect each server of the rack to the two ToRs. The dual cable may be interchangeable. In one embodiment, the dual cable may be configured to broadcast data traffic from a device (e.g., server) to a first ToR and a second ToR. The dual cable may further be configured to switch incoming data traffic from a first ToR to a second ToR, for example if the first ToR has failed or needs to be serviced. In an embodiment, circuitry to implement this switching capability may be embedded in a Quad Small Form-factor Pluggable (QSFP)-based DAC cable. The circuitry may be configured to switch data traffic from one ToR device to the other ToR device.

In the case of lower speed data, such as for control plane data, it may not be necessary to implement a fast switching methodology to indicate which of the dual ToRs should be primary. For example, it may not be necessary for the dual ToRs to be configured to determine which ToR should be primary and generate an indication using a control signal, or to provide methods of communication from the ToR to the NIC such as using ON/OFF of the link, or using BFD between the ToR and the NIC.

In some embodiments, the switch device in the cable itself may be configured to make the decision to switch between ToRs. In one embodiment, the switch device may be accompanied by a microcontroller unit (MCU) device configured to control various aspects of auto-negotiation and link training. This MCU device may execute code that is modifiable. Interactions with the switch device state can be used to determine if a link is up/down or in some other intermediate state. The presence of a fully trained link may be interpreted as the link being in an UP state and hence may be used to allow the switch device to determine which link will be used based on a flexible and programmable model. In some embodiments, the switch device with MCU may be configured to work in conjunction with other mechanisms deployed by the NIC or ToR.

In various embodiments disclosed herein, the switching of active and standby ToRs can be greatly simplified to avoid the ToRs having to communicate with one another to negotiate which will be active or standby. One problem with using dual devices is that both devices may believe that they are the active device and act as the active device. Alternatively, both devices may believe that the other device is the active device, and act as the standby device, in which case severe data communications problems may result. The disclosed techniques allow for maintaining network connectivity to one or more servers of a rack if its connection to the ToR fails or if one of the ToRs is serviced/replaced, without the need for coordination between ToRs, while avoiding the possibility of both ToRs acting as active or standby devices.

By using a dual cable with the ToR switching techniques, from the server perspective, only a single link to a single ToR is observed because data is sent to the multiplexer which switches between the ToRs. No changes are thus required on the server side. A switchover of active/standby ToRs at one server may not affect other servers in the rack or row. In some embodiments, a rack may support a mix of servers selecting between the primary and the secondary ToR.

It should be understood that the methods described herein can be extended to two or more network devices such as ToRs. The described examples are illustrated using two ToRs for simplicity; however, the techniques may be extended to two or more ToRs (or other network devices) in various implementations. It should also be understood that the described techniques may be used using connectors other than QSFP connectors.

FIG. 1 illustrates an example computing environment in which the embodiments described herein may be implemented. FIG. 1 illustrates a data center 100 that configured to provide computing resources to users 100 a, 100 b, or 100 c (which may be referred herein singularly as “a user 100” or in the plural as “the users 100”) via user computers 102 a,102 b, and 102 c (which may be referred herein singularly as “a computer 102” or in the plural as “the computers 102”) via a communications network 130. The computing resources provided by the data center 100 may include various types of resources, such as computing resources, data storage resources, data communication resources, and the like. Each type of computing resource may be general-purpose or may be available in a number of specific configurations. For example, computing resources may be available as virtual machines. The virtual machines may be configured to execute applications, including Web servers, application servers, media servers, database servers, and the like. Data storage resources may include file storage devices, block storage devices, and the like. Each type or configuration of computing resource may be available in different configurations, such as the number of processors, and size of memory and/or storage capacity. The resources may in some embodiments be offered to clients in units referred to as instances, such as virtual machine instances or storage instances. A virtual computing instance may be referred to as a virtual machine and may, for example, comprise one or more servers with a specified computational capacity (which may be specified by indicating the type and number of CPUs, the main memory size and so on) and a specified software stack (e.g., a particular version of an operating system, which may in turn run on top of a hypervisor).

Data center 100 may include servers 116 a, 116 b, and 116 c (which may be referred to herein singularly as “a server 116” or in the plural as “the servers 116”) that provide computing resources available as virtual machines 118 a and 118 b (which may be referred to herein singularly as “a virtual machine 118” or in the plural as “the virtual machines 118”). The virtual machines 118 may be configured to execute applications such as Web servers, application servers, media servers, database servers, and the like. Other resources that may be provided include data storage resources (not shown on FIG. 1) and may include file storage devices, block storage devices, and the like. Servers 116 may also execute functions that manage and control allocation of resources in the data center, such as a controller 115. Controller 115 may be a fabric controller or another type of program configured to manage the allocation of virtual machines on servers 116.

Referring to FIG. 1, communications network 130 may, for example, be a publicly accessible network of linked networks and may be operated by various entities, such as the Internet. In other embodiments, communications network 130 may be a private network, such as a corporate network that is wholly or partially inaccessible to the public.

Communications network 130 may provide access to computers 102. Computers 102 may be computers utilized by users 100. Computer 102 a,102 b or 102 c may be a server, a desktop or laptop personal computer, a tablet computer, a smartphone, a set-top box, or any other computing device capable of accessing data center 100. User computer 102 a or 102 b may connect directly to the Internet (e.g., via a cable modem). User computer 102 c may be internal to the data center 100 and may connect directly to the resources in the data center 100 via internal networks. Although only three user computers 102 a,102 b, and 102 c are depicted, it should be appreciated that there may be multiple user computers.

Computers 102 may also be utilized to configure aspects of the computing resources provided by data center 100. For example, data center 100 may provide a Web interface through which aspects of its operation may be configured through the use of a Web browser application program executing on user computer 102. Alternatively, a stand-alone application program executing on user computer 102 may be used to access an application programming interface (API) exposed by data center 100 for performing the configuration operations.

Servers 116 may be configured to provide the computing resources described above. One or more of the servers 116 may be configured to execute a manager 110 a or 110 b (which may be referred herein singularly as “a manager 110” or in the plural as “the managers 110”) configured to execute the virtual machines. The managers 110 may be a virtual machine monitor (VMM), fabric controller, or another type of program configured to enable the execution of virtual machines 118 on servers 116, for example.

It should be appreciated that although the embodiments disclosed above are discussed in the context of virtual machines, other types of implementations can be utilized with the concepts and technologies disclosed herein. For example, the embodiments disclosed herein might also be utilized with computing systems that do not utilize virtual machines.

In the example data center 100 shown in FIG. 1, a router 111 may be utilized to interconnect the servers 116 a and 116 b. Router 111 may also be connected to gateway 140, which is connected to communications network 130. Router 111 may manage communications within networks in data center 100, for example, by forwarding packets or other data communications as appropriate based on characteristics of such communications (e.g., header information including source and/or destination addresses, protocol identifiers, etc.) and/or the characteristics of the private network (e.g., routes based on network topology, etc.). It will be appreciated that, for the sake of simplicity, various aspects of the computing systems and other devices of this example are illustrated without showing certain conventional details. Additional computing systems and other devices may be interconnected in other embodiments and may be interconnected in different ways.

It should be appreciated that the network topology illustrated in FIG. 1 has been greatly simplified and that many more networks and networking devices may be utilized to interconnect the various computing systems disclosed herein. These network topologies and devices should be apparent to those skilled in the art.

It should also be appreciated that data center 100 described in FIG. 1 is merely illustrative and that other implementations might be utilized. Additionally, it should be appreciated that the functionality disclosed herein might be implemented in software, hardware or a combination of software and hardware. Other implementations should be apparent to those skilled in the art. It should also be appreciated that a server, gateway, or other computing device may comprise any combination of hardware or software that can interact and perform the described types of functionality, including without limitation desktop or other computers, database servers, network storage devices and other network devices, tablets, and various other devices that include appropriate communication capabilities. In addition, the functionality provided by the illustrated modules may in some embodiments be combined in fewer modules or distributed in additional modules. Similarly, in some embodiments the functionality of some of the illustrated modules may not be provided and/or other additional functionality may be available.

FIG. 2A illustrates an example topology of a network implementing a dual cable. In one embodiment, a dual cable may have 4 TX, 4 RX, and one or more control lines. For example, the control lines may include a Clock and a I2C line. FIG. 2A illustrates a resilient network topology with switching implemented at the QSFP cable. Illustrated are two Tier-0 ToR network elements 260 and 270. Switching chip 230 may be implemented in the dual cable that implements Layer-1 switching within the cable. One of dual ToRs 260 and 270 are connected to server 210 based on the switching.

In some embodiments, control and status signaling may be implemented to indicate an active communication path corresponding to one of two ToRs. In some embodiments, the control and status signaling may be implemented as an in-band signal. In other embodiments, out of band control and status signaling may be implemented using existing conductors in the dual cable.

In one embodiment, the control and status signal can be a 2-level active/standby signal or a serial bus with multi-master capability. Changes in the active/standby state can be driven by either ToR. In some embodiments, the secondary or slave ToR may initiate a switch if the primary ToR fails to generate heartbeat messages for a predetermined threshold.

FIG. 2B illustrates another example topology of a network implementing a dual cable. In an embodiment, a dual cable may have 4 TX and 4 RX, but does not provide control lines from the ToRs. In this example, the NIC 215 may determine whether to control the switch device 230 to switch between ToRs 260 or 270 based on the presence or absence of a BFD heartbeat for a predetermined threshold, which indicates whether the currently active ToR is communicating properly.

FIG. 3A illustrates an example software-based switching mechanism as disclosed herein. In this example, a dual cable with connector 320 may be connected to diverse network interfaces at ToR1 330 and ToR2 340. As shown in FIG. 3A, ToR1 330 and ToR2 340 need not be directly communicatively coupled. Connector 320 may be connected to the server-side interface and receive data, control, and optionally power. A switch 340 is controllable via a control signal to select one of the network interfaces.

In an embodiment, a process may be executed to identify which ToR is the active switch and which ToR is the standby switch. The active and standby roles may determine whether the server side will receive data from ToR1 330 or ToR2 340. The functionality for determining the active ToR may be implemented based on routing functionality on the ToRs. The servers and their associated network interface devices such as the NIC thus do not require new functionality.

In an embodiment, the same data may be transmitted to both ToRs from the network. The MUX mechanism 310 and controller 315 in the connector 320 may be configured to switch between the ToRs. In some embodiments, the MUX mechanism 310 and controller 315 may determine which ToR is active if an error or some type of inconsistency is detected, for example if the connection to one of the ToRs is faulty. When the ToR is switched, the Border Gateway Protocol (BGP) status of the TORs may be updated.

In some embodiments, the switching mechanism may be implemented as a device such as a chip that includes multiplexing capability. In one example, a SERDES based multiplexer may be implemented that is configured to select a primary ToR. In one example, the multiplexer can be configured to provide 8 individual TX/RX lanes on a first side, and 8 individual TX/RX lanes on a second side.

FIG. 3B illustrates an example MUX 310 that may be connected to diverse network interfaces at ToR1 330 and ToR2 340. As shown in FIG. 3A, ToR1 310 has a transmit interface 360 and receive interface 362, and ToR2 320 has a transmit interface 364 and receive interface 466. MUX 310 may be connected to the server-side interface 357 via NIC TX 359 and NIC RX 355.

In an embodiment, the same data may be transmitted to both ToRs from the network from NIC TX 350. NIC RX 355 only receives data from the active ToR. In an embodiment, the properties and utilities of the networking protocols, such as Ethernet protocols, may be used to enable a software-based mechanism to forward data from the active ToR to the NIC RX 355. A utility for discovery and pinging network devices such as ARPing may be used to identify the active ToR. For example, ping packets may be transmitted to probe hosts using Address Resolution Protocol (ARP). The pinged information allows for the association of the MAC address of the host and the receiving MAC address for the active ToR. This allows hosts to be resolved by MAC addresses, and both ToRs can determine, based on the pinged information, whether they are an active or passive ToR. Thus, only traffic originating from the active ToR will be forwarded to NIC RX 355.

For example, both ToRs may send an ARPing request to the server. Only the ARPing request from the active ToR is received by the server since the MUX is only allowing traffic from the active ToR. An ARPing reply may be sent by the server to the active ToR that identifies its MAC address, thus permitting packets with the correct destination MAC address to be forwarded on the network. The standby ToR still receives the ARPing reply since the MUX broadcasts to both ToRs, but the standby ToR can determine based on the ARPing reply packet being addressed to the active ToR that it is not the active ToR. Going forward, packets with the incorrect destination MAC address can be dropped. Because each ToR can see the ARPing response packet and independently determine which is the active ToR, there is little or no performance loss.

Other protocols may be used to allow the active ToR to be identified or otherwise provide communications to the server. For example, BGP may be used in some embodiments to allow the active ToR to forward traffic to the server. For example, if the standby ToR receives any packets that are addressed to the server, the standby ToR recognizes that it is the standby ToR, encapsulates the packet and forwards the packet to the active ToR. The active ToR receives the encapsulated packet, identifies that it should be forwarded to the server, decapsulates the packet, and forwards the packet to the server via its active link.

Turning now to FIG. 4, illustrated is an example operational procedure for implementing a fault resilient mechanism in accordance with the present disclosure. The operational procedure may be implemented in a system comprising plurality of servers and at least two top-of-rack switches. Referring to FIG. 4, operation 401 illustrates on each of the two top-of-rack switches, duplicating data signals at network interfaces of the two top-of-rack switches. In an embodiment, each of the network interfaces are communicatively coupled to a data cable having a switching mechanism configured to select one of the network interfaces of the two top-of-rack switches. In an embodiment, the data cable is communicatively coupled to one of the plurality of servers.

Operation 401 may be followed by operation 403. Operation 403 illustrates activating a control signal to indicate an active communication path from a first of the two top- of-rack switches to the communicatively coupled server. In an embodiment, the active communication path corresponds to a first of the two network interfaces.

Operation 403 may be followed by operation 405. Operation 405 illustrates in response to detecting a failure of the active communication path, modifying the control signal to indicate a switch to a second of the two network interfaces corresponding to a second of the two top-of-rack switches.

Operation 405 may be followed by operation 407. Operation 407 illustrates in response to the modified control signal, switching, by the switching mechanism of the data cable, the active communication path to the second of the two network interfaces.

In an embodiment, the data cable is a Direct Attach Cable (DAC). In an embodiment, the data cable is a QSFP28 cable. In an embodiment, the control signal is an out-of-band control plane signal implemented using a conductor on the DAC. In some embodiments, the out-of-band control plane signal is one of a 2-level signal or a serial bus. In an embodiment, the control signal is carried on a I2C bus of the data cable

In an embodiment, detecting the failure of the active communication path and modifying the control signal is performed by at least one of the two top-of-rack switches. In some embodiments, detecting the failure of the active communication path and modifying the control signal is performed by a network interface card (NIC) of the communicatively coupled server.

In an embodiment, the failure is detected when a network element of the active communication path fails to generate heartbeat messages for a predetermined duration.

Turning now to FIG. 4, illustrated is an example operational procedure for implementing a fault resilient mechanism in accordance with the present disclosure. It should be understood that the operations of the methods disclosed herein are not presented in any particular order and that performance of some or all of the operations in an alternative order(s) is possible and is contemplated. The operations have been presented in the demonstrated order for ease of description and illustration. Operations may be added, omitted, and/or performed simultaneously, without departing from the scope of the appended claims.

It also should be understood that the illustrated methods can end at any time and need not be performed in their entireties. Some or all operations of the methods, and/or substantially equivalent operations, can be performed by execution of computer-readable instructions included on a computer-storage media, as defined below. The term “computer-readable instructions,” and variants thereof, as used in the description and claims, is used expansively herein to include routines, applications, application modules, program modules, programs, components, data structures, algorithms, and the like. Computer-readable instructions can be implemented on various system configurations, including single-processor or multiprocessor systems, minicomputers, mainframe computers, personal computers, hand-held computing devices, microprocessor-based, programmable consumer electronics, combinations thereof, and the like.

Thus, it should be appreciated that the logical operations described herein are implemented (1) as a sequence of computer implemented acts or program modules running on a computing system and/or (2) as interconnected machine logic circuits or circuit modules within the computing system. The implementation is a matter of choice dependent on the performance and other requirements of the computing system. Accordingly, the logical operations described herein are referred to variously as states, operations, structural devices, acts, or modules. These operations, structural devices, acts, and modules may be implemented in software, in firmware, in special purpose digital logic, and any combination thereof.

For example, the operations of the routine 700 are described herein as being implemented, at least in part, by modules running the features disclosed herein and can be a dynamically linked library (DLL), a statically linked library, functionality produced by an application programing interface (API), a compiled program, an interpreted program, a script or any other executable set of instructions. Data can be stored in a data structure in one or more memory components. Data can be retrieved from the data structure by addressing links or references to the data structure.

Although the following illustration refers to the components of the figures, it can be appreciated that the operations of the routine 400 may be also implemented in many other ways. For example, the routine 400 may be implemented, at least in part, by a processor of another remote computer or a local circuit. In addition, one or more of the operations of the routine 400 may alternatively or additionally be implemented, at least in part, by a chipset working alone or in conjunction with other software modules. In the example described below, one or more modules of a computing system can receive and/or process the data disclosed herein. Any service, circuit or application suitable for providing the techniques disclosed herein can be used in operations described herein.

The operational procedure may be implemented in a system comprising a plurality of servers and at least two network devices, the servers communicatively coupled to network interfaces of the network devices using a plurality of data cables, the data cables each comprising a switch device configured to switch communication paths to the coupled network devices. Each of the data cables may communicatively couple each of the network devices to one of the plurality of servers so that each of the servers has a communications path to each of the network devices and a switchable communications path from each of the network devices. In an embodiment, the network devices do not arbitrate active/passive status via direct communication. Referring to FIG. 4, operation 401 illustrates determining validity of a communication path from a first of the network devices to a first of the communicatively coupled servers, the communication path corresponding to a first of the data cables connecting a first of the network interfaces to the first communicatively coupled server.

Operation 401 may be followed by operation 403. Operation 403 illustrates causing the switch device of the first data cable to connect the first network interface to the first communicatively coupled server when the communication path from the first network device is determined to be valid.

Operation 403 may be followed by operation 405. Operation 405 illustrates sending, by the first network device, a request packet to the first communicatively coupled server.

Operation 405 may be followed by operation 407. Operation 407 illustrates sending, by a second of the network devices, a request packet to the first communicatively coupled server.

Operation 407 may be followed by operation 409. Operation 409 illustrates receiving, by the first and second network devices, a reply packet from the first communicatively coupled server, wherein the reply packet is generated based only on the request packet sent by the first network device based on the first data cable connecting the first network interface to the first communicatively coupled server.

Operation 409 may be followed by operation 411. Operation 411 illustrates based on data contained in the reply packet indicating that the request packet sent by the first network device was acknowledged, determining, by the first network device, that the first network device is an active network device, wherein the determining is performed independently of communication with the second network device.

Operation 411 may be followed by operation 413. Operation 413 illustrates forwarding, by the first network device, data packets to the first communicatively coupled server based on its status as the active network device.

In an embodiment, the method further comprises in response to detecting a failure of the communication path from the first network device, causing the switch device of the first data cable to connect a second network interface to the first communicatively coupled server, the second network interface providing a communication path from the second of the network devices to the first communicatively coupled server.

In an embodiment, the method further comprises:

sending, by the first and second network devices, a second request packet;

receiving, by the first communicatively coupled server, only the request packet sent by the second network device based on the first data cable connecting the second network interface to the first communicatively coupled server;

receiving, by the first and second network devices, a second reply packet from the first communicatively coupled server, wherein the second reply packet is generated based only on the request packet sent by the second network device;

based on data contained in the second reply packet, determining, by the first and second network devices, that the second network device is an active network device; and

forwarding, by the second network device, data packets to the first communicatively coupled server based on its status as the active network device.

In an embodiment, the request and reply packets are ARPing packets.

In an embodiment, the request and reply packets are BGP packets.

In an embodiment, determining that the first network device is an active top-of-rack switch is based on the reply packet specifying the first network device as a destination address for the reply packet.

In an embodiment, determining validity is determined based on a network element of the communication path generating heartbeat messages for a predetermined duration.

In an embodiment, the method further comprises:

receiving, by the second network device, a data packet addressed to the first communicatively coupled server;

encapsulating, by the second network device, the data packet addressed to the first communicatively coupled server; and

forwarding, by the second network device, the encapsulated data packet to the first network device.

In an embodiment, the method further comprises:

receiving, by the first network device, the encapsulated data packet;

decapsulating, by the first network device, the encapsulated data packet; and

forwarding, by the first network device, the decapsulated data packet to the first communicatively coupled server

Turning now to FIG. 5, illustrated is an example operational procedure for implementing a fault resilient mechanism in accordance with the present disclosure. The operational procedure may be implemented in a system comprising plurality of servers and at least two switches. A plurality of data cables may each have a switching device. The servers may be communicatively coupled to network interfaces of the switches using the plurality of data cables. The switch devices may be configured to switch communication paths between the switches. Each of the data cables may be communicatively couple the switches to one of the plurality of servers. In an embodiment, the switch device of a first data cable connects a first network interface to a first communicatively coupled server when the communication path from a first of the switches to a first of the communicatively coupled servers is determined to be valid. The communication path corresponding to a first of the data cables may connect a first network interface to the first communicatively coupled server.

Referring to FIG. 5, operation 501 illustrates send, by the first switch, a request packet.

Operation 501 may be followed by operation 503. Operation 503 illustrates send, by a second of the switches, a request packet.

Operation 503 may be followed by operation 505. Operation 505 illustrates receive, by the first and second switches, a reply packet from the first communicatively coupled server.

Operation 505 may be followed by operation 507. Operation 507 illustrates determine, by the first switch, that the first switch is an active switch.

Operation 507 may be followed by operation 509. Operation 509 illustrates forward, by the first switch, data packets to the first communicatively coupled server based on its status as the active switch.

In an embodiment, the switches are further configured to:

in response to detecting a failure of the communication path from the first switch, cause the switch device of the first data cable to connect a second network interface to the first communicatively coupled server, the second network interface providing a communication path from the second of switches to the first communicatively coupled server.

In an embodiment, the switches are further configured to:

send, by the first and second switches, a second request packet;

receive, by the first communicatively coupled server, only the request packet sent by the second switch based on the first data cable connecting the second network interface to the first communicatively coupled server;

receive, by the first and second switches, a second reply packet from the first communicatively coupled server, wherein the second reply packet is generated based only on the request packet sent by the second switch;

based on data contained in the second reply packet, determine, by the first and second switches, that the second switch is an active switch; and

forward, by the second switch, data packets to the first communicatively coupled server based on its status as the active switch.

In an embodiment, the request and reply packets are ARPing packets or BGP packets.

Turning now to FIG. 6, illustrated is an example operational procedure for implementing a fault resilient mechanism in accordance with the present disclosure. The operational procedure may be implemented in a system comprising plurality of servers and at least two network devices. The network device may have network interfaces that are communicatively coupled to a server using a data cable comprising a switch device configured to switch communication paths to the network device. The data cable may communicatively couple the network device to the server so that the server has a switchable communications path to the network device and a second network device. In an embodiment, the network device and the second network device do not arbitrate active/passive status via direct communication Referring to FIG. 6, operation 601 illustrates send a request packet.

Operation 601 may be followed by operation 603. Operation 603 illustrates receive a reply packet from a communicatively coupled server. In an embodiment, the reply packet is generated based only on the request packet sent by the network device based on the data cable connecting the network device to the communicatively coupled server.

Operation 603 may be followed by operation 605. Operation 605 illustrates based on data contained in the reply packet indicating that the request packet sent by the network device was acknowledged, determine, by the network device, that it is an active network device of a plurality of network devices.

Operation 605 may be followed by operation 607. Operation 607 illustrates forward, by the network device, data packets to the communicatively coupled server based on its status as the active network device.

In an embodiment, a plurality of servers are communicatively coupled to network interfaces of the plurality of network devices using a plurality of data cables, the data cables each comprising a switch device configured to switch communication paths to the coupled network devices, each of the data cables communicatively coupling each of the network devices to one of the plurality of servers so that each of the servers has a communications path to each of the network devices and a switchable communications path from each of the network devices.

In an embodiment, the data cables are Direct Attach Cables (DACs).

In an embodiment, the request and reply packets are ARPing packets.

In an embodiment, the request and reply packets are BGP packets.

In an embodiment, determining that the network device is an active network device is based on the reply packet specifying the network device as a destination address for the reply packet.

In an embodiment, the network device is further configured to:

send a second request packet;

receive a second reply packet from the first communicatively coupled server, wherein the second reply packet; and

based on data contained in the second reply packet, determine, by the network device, that it is a standby network device of a plurality of network devices.

The various aspects of the disclosure are described herein with regard to certain examples and embodiments, which are intended to illustrate but not to limit the disclosure. It should be appreciated that the subject matter presented herein may be implemented as a computer process, a computer-controlled apparatus, a computing system, an article of manufacture, such as a computer-readable storage medium, or a component including hardware logic for implementing functions, such as a field-programmable gate array (FPGA) device, a massively parallel processor array (MPPA) device, a graphics processing unit (GPU), an application-specific integrated circuit (ASIC), a multiprocessor System-on-Chip (MPSoC), etc. A component may also encompass other ways of leveraging a device to perform a function, such as, for example, a) a case in which at least some tasks are implemented in hard ASIC logic or the like; b) a case in which at least some tasks are implemented in soft (configurable) FPGA logic or the like; c) a case in which at least some tasks run as software on FPGA software processor overlays or the like; d) a case in which at least some tasks run as software on hard ASIC processors or the like, etc., or any combination thereof. A component may represent a homogeneous collection of hardware acceleration devices, such as, for example, FPGA devices. On the other hand, a component may represent a heterogeneous collection of different types of hardware acceleration devices including different types of FPGA devices having different respective processing capabilities and architectures, a mixture of FPGA devices and other types hardware acceleration devices, etc.

Those skilled in the art will also appreciate that the subject matter described herein may be practiced on or in conjunction with other computer system configurations beyond those described herein, including multiprocessor systems. The embodiments described herein may also be practiced in distributed computing environments, where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices.

Networks established by or on behalf of a user to provide one or more services (such as various types of cloud-based computing or storage) accessible via the Internet and/or other networks to a distributed set of clients may be referred to as a service provider. Such a network may include one or more data centers such as data center 100 illustrated in FIG. 1, which are configured to host physical and/or virtualized computer servers, storage devices, networking equipment and the like, that may be used to implement and distribute the infrastructure and services offered by the service provider.

In some embodiments, a server that implements a portion or all of one or more of the technologies described herein, including the techniques to implement the capturing of network traffic may include a general-purpose computer system that includes or is configured to access one or more computer-accessible media. FIG. 8 illustrates such a general-purpose computing device 800. In the illustrated embodiment, computing device 800 includes one or more processors 810 a, 810 b, and/or 810 n (which may be referred herein singularly as “a processor 810” or in the plural as “the processors 810”) coupled to a system memory 820 via an input/output (I/O) interface 830. Computing device 800 further includes a network interface 840 coupled to I/O interface 830.

In various embodiments, computing device 800 may be a uniprocessor system including one processor 810 or a multiprocessor system including several processors 810 (e.g., two, four, eight, or another suitable number). Processors 810 may be any suitable processors capable of executing instructions. For example, in various embodiments, processors 810 may be general-purpose or embedded processors implementing any of a variety of instruction set architectures (ISAs), such as the x86, PowerPC, SPARC, or MIPS ISAs, or any other suitable ISA. In multiprocessor systems, each of processors 810 may commonly, but not necessarily, implement the same ISA.

System memory 820 may be configured to store instructions and data accessible by processor(s) 810. In various embodiments, system memory 820 may be implemented using any suitable memory technology, such as static random access memory (SRAM), synchronous dynamic RAM (SDRAM), nonvolatile/Flash-type memory, or any other type of memory. In the illustrated embodiment, program instructions and data implementing one or more desired functions, such as those methods, techniques and data described above, are shown stored within system memory 820 as code 825 and data 826.

In one embodiment, I/O interface 880 may be configured to coordinate I/O traffic between the processor 810, system memory 820, and any peripheral devices in the device, including network interface 840 or other peripheral interfaces. In some embodiments, I/O interface 880 may perform any necessary protocol, timing, or other data transformations to convert data signals from one component (e.g., system memory 820) into a format suitable for use by another component (e.g., processor 810). In some embodiments, I/O interface 880 may include support for devices attached through various types of peripheral buses, such as a variant of the Peripheral Component Interconnect (PCI) bus standard or the Universal Serial Bus (USB) standard, for example. In some embodiments, the function of I/O interface 880 may be split into two or more separate components. Also, in some embodiments some or all of the functionality of I/O interface 880, such as an interface to system memory 820, may be incorporated directly into processor 810.

Network interface 840 may be configured to allow data to be exchanged between computing device 800 and other device or devices 860 attached to a network or network(s) 850, such as other computer systems or devices as illustrated in FIGS. 1 through 4, for example. In various embodiments, network interface 840 may support communication via any suitable wired or wireless general data networks, such as types of Ethernet networks, for example. Additionally, network interface 840 may support communication via telecommunications/telephony networks such as analog voice networks or digital fiber communications networks, via storage area networks such as Fibre Channel SANs or via any other suitable type of network and/or protocol.

In some embodiments, system memory 820 may be one embodiment of a computer-accessible medium configured to store program instructions and data as described above for FIGS. 1-7 for implementing embodiments of the corresponding methods and apparatus. However, in other embodiments, program instructions and/or data may be received, sent or stored upon different types of computer-accessible media. A computer-accessible medium may include non-transitory storage media or memory media, such as magnetic or optical media, e.g., disk or DVD/CD coupled to computing device 800 via I/O interface 880. A non-transitory computer-accessible storage medium may also include any volatile or non-volatile media, such as RAM (e.g. SDRAM, DDR SDRAM, RDRAM, SRAM, etc.), ROM, etc., that may be included in some embodiments of computing device 800 as system memory 820 or another type of memory. Further, a computer-accessible medium may include transmission media or signals such as electrical, electromagnetic or digital signals, conveyed via a communication medium such as a network and/or a wireless link, such as may be implemented via network interface 840. Portions or all of multiple computing devices, such as those illustrated in FIG. 8, may be used to implement the described functionality in various embodiments; for example, software components running on a variety of different devices and servers may collaborate to provide the functionality. In some embodiments, portions of the described functionality may be implemented using storage devices, network devices, or special-purpose computer systems, in addition to or instead of being implemented using general-purpose computer systems. The term “computing device,” as used herein, refers to at least all these types of devices and is not limited to these types of devices.

Various storage devices and their associated computer-readable media provide non-volatile storage for the computing devices described herein. Computer-readable media as discussed herein may refer to a mass storage device, such as a solid-state drive, a hard disk or CD-ROM drive. However, it should be appreciated by those skilled in the art that computer-readable media can be any available computer storage media that can be accessed by a computing device.

By way of example, and not limitation, computer storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. For example, computer media includes, but is not limited to, RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-ROM, digital versatile disks (“DVD”), HD-DVD, BLU-RAY, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the computing devices discussed herein. For purposes of the claims, the phrase “computer storage medium,” “computer-readable storage medium” and variations thereof, does not include waves, signals, and/or other transitory and/or intangible communication media, per se.

Encoding the software modules presented herein also may transform the physical structure of the computer-readable media presented herein. The specific transformation of physical structure may depend on various factors, in different implementations of this description. Examples of such factors may include, but are not limited to, the technology used to implement the computer-readable media, whether the computer-readable media is characterized as primary or secondary storage, and the like. For example, if the computer-readable media is implemented as semiconductor-based memory, the software disclosed herein may be encoded on the computer-readable media by transforming the physical state of the semiconductor memory. For example, the software may transform the state of transistors, capacitors, or other discrete circuit elements constituting the semiconductor memory. The software also may transform the physical state of such components in order to store data thereupon.

As another example, the computer-readable media disclosed herein may be implemented using magnetic or optical technology. In such implementations, the software presented herein may transform the physical state of magnetic or optical media, when the software is encoded therein. These transformations may include altering the magnetic characteristics of particular locations within given magnetic media. These transformations also may include altering the physical features or characteristics of particular locations within given optical media, to change the optical characteristics of those locations. Other transformations of physical media are possible without departing from the scope and spirit of the present description, with the foregoing examples provided only to facilitate this discussion.

In light of the above, it should be appreciated that many types of physical transformations take place in the disclosed computing devices in order to store and execute the software components and/or functionality presented herein. It is also contemplated that the disclosed computing devices may not include all of the illustrated components shown in FIG. 8, may include other components that are not explicitly shown in FIG. 8, or may utilize an architecture completely different than that shown in FIG. 8.

Although the various configurations have been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended representations is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as example forms of implementing the claimed subject matter.

Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements, and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements, and/or steps are included or are to be performed in any particular embodiment. The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list.

While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions disclosed herein. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of certain of the inventions disclosed herein.

It should be appreciated any reference to “first,” “second,” etc. items and/or abstract concepts within the description is not intended to and should not be construed to necessarily correspond to any reference of “first,” “second,” etc. elements of the claims. In particular, within this Summary and/or the following Detailed Description, items and/or abstract concepts such as, for example, individual computing devices and/or operational states of the computing cluster may be distinguished by numerical designations without such designations corresponding to the claims or even other paragraphs of the Summary and/or Detailed Description. For example, any designation of a “first operational state” and “second operational state” of the computing cluster within a paragraph of this disclosure is used solely to distinguish two different operational states of the computing cluster within that specific paragraph—not any other paragraph and particularly not the claims.

In closing, although the various techniques have been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended representations is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as example forms of implementing the claimed subject matter. 

1. A method for routing data at a network comprising a plurality of servers and at least two network devices, the servers communicatively coupled to network interfaces of the network devices using a plurality of data cables, the data cables each comprising a switch device configured to switch communication paths to the coupled network devices, each of the data cables communicatively coupling each of the network devices to one of the plurality of servers so that each of the servers has a communications path to each of the network devices and a switchable communications path from each of the network devices, wherein the network devices do not arbitrate active/passive status via direct communication, the method comprising: determining validity of a communication path from a first of the network devices to a first of the communicatively coupled servers, the communication path corresponding to a first of the data cables connecting a first of the network interfaces to the first communicatively coupled server; causing the switch device of the first data cable to connect the first network interface to the first communicatively coupled server when the communication path from the first network device is determined to be valid; sending, by the first network device, a request packet to the first communicatively coupled server; sending, by a second of the network devices, a request packet to the first communicatively coupled server; receiving, by the first and second network devices, a reply packet from the first communicatively coupled server, wherein the reply packet is generated based only on the request packet sent by the first network device based on the first data cable connecting the first network interface to the first communicatively coupled server; based on data contained in the reply packet indicating that the request packet sent by the first network device was acknowledged, determining, by the first network device, that the first network device is an active network device, wherein the determining is performed independently of communication with the second network device; and forwarding, by the first network device, data packets to the first communicatively coupled server based on its status as the active network device.
 2. The method of claim 1, further comprising: in response to detecting a failure of the communication path from the first network device, causing the switch device of the first data cable to connect a second network interface to the first communicatively coupled server, the second network interface providing a communication path from the second of the network devices to the first communicatively coupled server.
 3. The method of claim 2, further comprising: sending, by the first and second network devices, a second request packet; receiving, by the first communicatively coupled server, only the request packet sent by the second network device based on the first data cable connecting the second network interface to the first communicatively coupled server; receiving, by the first and second network devices, a second reply packet from the first communicatively coupled server, wherein the second reply packet is generated based only on the request packet sent by the second network device; based on data contained in the second reply packet, determining, by the first and second network devices, that the second network device is an active network device; and forwarding, by the second network device, data packets to the first communicatively coupled server based on its status as the active network device.
 4. The method of claim 1, wherein the request and reply packets are ARPing packets.
 5. The method of claim 1, wherein the request and reply packets are BGP packets.
 6. The method of claim 1, wherein determining that the first network device is an active top-of-rack switch is based on the reply packet specifying the first network device as a destination address for the reply packet.
 7. The method of claim 1, wherein determining validity is determined based on a network element of the communication path generating heartbeat messages for a predetermined duration.
 8. The method of claim 1, further comprising: receiving, by the second network device, a data packet addressed to the first communicatively coupled server; encapsulating, by the second network device, the data packet addressed to the first communicatively coupled server; and forwarding, by the second network device, the encapsulated data packet to the first network device.
 9. The method of claim 8, further comprising: receiving, by the first network device, the encapsulated data packet; decapsulating, by the first network device, the encapsulated data packet; and forwarding, by the first network device, the decapsulated data packet to the first communicatively coupled server.
 10. A system comprising: a plurality of servers; at least two switches; and a plurality of data cables each having a switching device, the servers communicatively coupled to network interfaces of the switches using the plurality of data cables, the switch devices configured to switch communication paths between the switches, each of the data cables communicatively coupling the switches to one of the plurality of servers so that each of the servers has a communications path to each of the switches and a switchable communications path from each of the switches, wherein the switch device of a first data cable connects a first network interface to a first communicatively coupled server when the communication path from a first of the switches to a first of the communicatively coupled servers is determined to be valid, the communication path corresponding to a first of the data cables connecting a first network interface to the first communicatively coupled server; the switches configured to: send, by the first switch, a request packet; send, by a second of the switches, a request packet; receive, by the first and second switches, a reply packet from the first communicatively coupled server, wherein the reply packet is generated based only on the request packet sent by the first switch based on the first data cable connecting the first network interface to the first communicatively coupled server; based on data contained in the reply packet indicating that the request packet sent by the first switch was acknowledged, determine, by the first switch, that the first switch is an active switch; and forward, by the first switch, data packets to the first communicatively coupled server based on its status as the active switch.
 11. The system of claim 10, wherein the switches are further configured to: in response to detecting a failure of the communication path from the first switch, cause the switch device of the first data cable to connect a second network interface to the first communicatively coupled server, the second network interface providing a communication path from the second of switches to the first communicatively coupled server.
 12. The system of claim 11, wherein the switches are further configured to: send, by the first and second switches, a second request packet; receive, by the first communicatively coupled server, only the request packet sent by the second switch based on the first data cable connecting the second network interface to the first communicatively coupled server; receive, by the first and second switches, a second reply packet from the first communicatively coupled server, wherein the second reply packet is generated based only on the request packet sent by the second switch; based on data contained in the second reply packet, determine, by the first and second switches, that the second switch is an active switch; and forward, by the second switch, data packets to the first communicatively coupled server based on its status as the active switch.
 13. The system of claim 10, wherein the request and reply packets are ARPing packets or BGP packets.
 14. A network device, network interfaces of the network device communicatively coupled to a server using a data cable comprising a switch device configured to switch communication paths to the network device, the data cable communicatively coupling the network device to the server so that the server has a switchable communications path to the network device and a second network device, wherein the network device and the second network device do not arbitrate active/passive status via direct communication, the network device configured to: send a request packet; receive a reply packet from a communicatively coupled server, wherein the reply packet is generated based only on the request packet sent by the network device based on the data cable connecting the network device to the communicatively coupled server; based on data contained in the reply packet indicating that the request packet sent by the network device was acknowledged, determine, by the network device, that it is an active network device of a plurality of network devices; and forward, by the network device, data packets to the communicatively coupled server based on its status as the active network device.
 15. The network device of claim 14, wherein a plurality of servers are communicatively coupled to network interfaces of the plurality of network devices using a plurality of data cables, the data cables each comprising a switch device configured to switch communication paths to the coupled network devices, each of the data cables communicatively coupling each of the network devices to one of the plurality of servers so that each of the servers has a communications path to each of the network devices and a switchable communications path from each of the network devices.
 16. The network device of claim 15, wherein the data cables are Direct Attach Cables (DACs).
 17. The network device of claim 14, wherein the request and reply packets are ARPing packets.
 18. The network device of claim 14, wherein the request and reply packets are BGP packets.
 19. The network device of claim 14, wherein determining that the network device is an active network device is based on the reply packet specifying the network device as a destination address for the reply packet.
 20. The network device of claim 14, further configured to: send a second request packet; receive a second reply packet from the first communicatively coupled server, wherein the second reply packet; and based on data contained in the second reply packet, determine, by the network device, that it is a standby network device of a plurality of network devices. 